Device for preparing a copy by means of latent electrostatic images



Oct. 16, 1962 W. LIMBERGER DEVICE FOR PREPARING A COPY BY MEANS OFLATENT ELECTROSTATIC IMAGES Filed OOb. 22, 1957 5 //V VENTOR.

AENT

United States Patent @hice 3,058,485 Patented Oct.- 16, 1962 3,858,405DEVICE FOR PREPARING A CGPY BY MEANS F LATENT ELECTRSTATIC IMAGES WalterLimberger, Hamburg, Germany, assigner to Lumoprint Zindler KG., Hamburg,Germany, a company of Germany Filed Oct. 22, 1957, Ser. No. 691,691Claims priority, application Germany Oct. 22, 1956 12 Claims. (Cl.95-1.7)

The invention relates to a device for preparing a copy by means oflatent electrostatic images, in which are provided a device for formingthe xerographic layer of the copy sheet, an illuminating device fortransferring an image from a master sheet to the Xerographic layer, adistributing device for the developer, which consists of carrierparticles of magnetisable material and toner, as well as a fusingdevice.

The invention is directed to the problem of improving Vknown apparatusas regards the supply of the toner to the xerographic layer and theconstruction of the apparatus,

particularly the heating device.

This problem is solved according to the invention in that, between thexerographic layer, which carries the electrostatic image, and adistributing device one or more magnets are arranged which are movedrelatively to the Xerographic layer and pick up the developer for thepurpose of transferring the toner to the xerographic layer.

In a preferred embodiment, several magnets are cornbined into a magnetroller from which the lines of force pass radially outwardssubstantially perpendicular to the axis of the roller. This roller isformed, advantageously, by several, erg. bar-shaped, magnets securedapproximate- 1y at their neutral zones to a shaft in planes runningperpendicular to the shaft axis. It will often suiiice to provide asimple bar-shaped magnet in each of these planes, all the magnetssecured to the shaft being arranged parallel to one another. Theroller-shaped device is completed by a'cylinder of non-magnetizablematerial mounted concentrically on the shaft, the front faces of thepole pieces of the magnets lying in the outer covering surface thereof.

The magnet arrangement can consist of permanent magnets or ofelectro-magnets. Furthermore, in a particularly advantageous embodiment,the invention provides for the similarly polarized magnets to bearranged side-byside. There is also the possibility of oppositelypolarizing the magnets which are arranged side-by-Side. The similarpolarization has the advantage that a uniform, substantially radialfield is produced at the outer circumference of the magnet arrangementat least in the axially extending sections.

The copy sheet is guided in the region of the magnetic array in asurface which runs parallel to at least one section of the surfaceenvelope of the solid of rotation defined by the movement of themagnetic array. 'Ihe invention provides, in an advantageous embodiment,an arrangement of the parts aifecting the magnetic flux so that thelines of force, in the section in which the sheet runs parallel to themoving magnetic array, pass perpendicularly through the sheet. The partsdirecting the ilux are so spaced that no developer particles arereleased by the magnetic array and developer particles falling to theguide path can drop into the collecting container.

`In accordance with a further feature of the invention, one or moreadditional magnets are further provided which increase the magneticiield of the magnetic array, for the purpose of directing the threadsformed from the developer behind the section in which the toner issupplied to the xerographic layer. 'Ihese additional magnets may beconstructed as electro-magnets whose exciter windings are polarized independence upon the rotation of the magnet roller if north and southpoles alternate along the circumference of the magnet roller. Thepolarization of the additional magnets is lthen effected through acommutator, for example, so that a field increasing the magnetic eld ofthe magnet roller is produced by the additional magnets. Preferably, theadditional magnets are arranged at a partition which subdivides thehousing of the apparatus into a iirst chamber, in -which the developmentof the latent electrostatic image occurs, and a second chamber,containing the heating device.

The guide path for the copy sheet through the heating device consists ofa preferably heatable perforated plate, in accordance with still anotherfeature of the invention; further heating elements may be disposed abovethis path. The suction side of a blower communicate with the spacebeneath the perforated plate which ensures a satisfactory guiding of thecopy sheet on the perforated plate, the sheet being held flat on theplate through the openings in the plate, and also an extraction of thefumes arising in the fusing of the pigment particles. This thereforesafely prevents the fumes from reaching other devices, particularly theforming device, in which the fumes would be detrimental. In the presentcase, the chamber containing the heating device is separated from theother parts of the apparatus, while at the same time a partial vacuum isproduced lthrough the connection of this chamber to the suction side ofa blower which prevents the escape of air from the chamber containingthe heating device into the other parts of the apparatus.

By arranging the forming device, which includes an illuminating device,as Well as the powder-distributing device, the magnetic array and theheating device behind one another, it is possible to construct thedevice as a desk-shaped table apparatus which, because of asubstantially V-shaped guide path for the copy sheet between theilluminating device and the exit slot, is of decreased height. Thisarrangement permits the construction of a readily operable apparatus, inwhich the master sheet and the copy sheet are guided parallel to oneanother through two directly adjacent slots in the apparatus and themaster sheet can be removed after illumination at the readily accessibleupper side of the apparatus.

Further advantages and features of the invention will appear from thefollowing description of an embodiment which is illustrated in theaccompanying drawing.

In the drawing:

FIG. l shows a side view lof the apparatus in section; and

FIG. 2 shows a plan view of the apparatus -according to FIG. 1, partlyin section on the line II-II of FIG. l.

The device according to the invention is provided in a desk-shapedhousing 1, at the front side of which two superposed slots Z, v3 arearranged for inserting the master sheet and the copy sheet. In the frontpart of the housing 1 a further `slot 4- is located at the upper side,through which the master sheet can be removed after illumination. A slot5 for removing the developed copy is located at the upper rear edge ofthe housing 1. At the upper side of the desk-shaped housing 1, behindthe removal slot 4 for the master, a cover `6 for the supply container18 for the developer is provided. This supply container is thus readilyaccessible so that its contents can be conveniently replenished.

A forming device 7, is located behind the slot 3, preferably comprisesseveral wires, to which the forming potential is applied, stretchedtransversely to the direction of advance of the layer support. Anassociated counterelectrode is indicated at 8 and is grounded. A cabinetcontaining a source of electrical potential for the electrodes 7, 8 isindicated at 9. At the upper wall of this cabinet there are located apair of insulators 10 from which electrical connections lead to theforming electrodes 7 and the counter-electrode 8.

A conventional illuminating device is arranged behind the forming deviceand consists, for example, of two illuminating tubes 11, reflectors 12and a glass plate 13 to which the master and a copy are guided rby theroller 14. The roller 14 preferably consists of rubber and has acovering of cotton fabric on its surface.

Behind the illuminating device the master is separated from the copy, sothat the master is guided along the arrows 15 to the outlet slot 4,whereas the copy sheet is further conveyed on the guide path 16. Theseparation of the master from the copy can be effected by hand, which isquite easy in the arrangement illustrated because of the readilyaccessible arrangement of the slot 4, or by some known mechanicalseparating device, not shown. The guide surface 17 for the master alsoserves as a wall lfor separating the section of the apparatus with theforming device and the heating device from the section of the apparatusin which are located the means for developing the electrostatic image.This part of the apparatus receives the supply container 18 'for thedeveloper and this supply container includes in its lower part a knowndevice, for example in the form of a roller 19, for dispensing ameasured supply of developer. This roller 19 is driven in dependenceupon the movement of other parts of the apparatus.

The developer consists of magnetizable carrier particles, for example,iron filings, and a toner formed by pigment particles. The compositionis preferably such that the developer is considerably enriched withtoner, since in the preferred construction the toner is transmitted tothe xerographic layer, whereas the carrier particles operate infunctional co-operation with a magnetic arrangement as conveying deviceswhich during the drive must be guided into the remaining toner. Thesupply container 18 may therefore be divided into two chambers, in oneof which contains only toner, so that a supply of toner alone or oftoner and carrier particles can be given as desired.

Under the distributing device there is disposed a magnetic array which,in the embodiment illustrated, is rollershaped. Bar magnets 21 are soarranged parallel and side-by-side on a shaft 20, mounted in thehousing, that the poles (provided, if desired, with supplemental polepieces not shown), project diametrically from the shaft 20. In theembodiment illustrated, all of the bar magnets 21 lying side-by-side are`magnetised in the same way, so that the north poles N are located atone side of the shaft and the south poles S at the opposite side.Furthermore, the shaft 20 is surrounded by a concentrically arrangedcylinder 33 of non-magnetiz-able material. This cylinder 33 rotates withthe shaft 20. The overall diameter of the cylinder 30 is so selectedthat the end faces of the poles or pole-pieces of the magnets 21 lie onthe outer periphery of the -cylinder 33.

By means of this arrangement, a strong magnetic eld is produced, in thesections extending axially of the cylinder 33 in which the pole piecesof the magnets 21 are located, which is directed substantially radiallyof the cylinder. The developer falls from the distributing device 19into this magnetic field and, as a result of the magnetizableconstitution of the carrier particles, forms threads or needle-shapedaccumulations projecting radially from the roller-shaped magnetic arraycorresponding to the lines of force of the magnetic field.

The magnetic array 20, 21, 33 rotates with such a velocity that itsperipheral speed is greater than the speed of advance of the copy. Thedeveloper accumulations on the circumference of the magnet roller aremade brush-shaped and guided over the xerographic layer of the copysheet which is advanced over the path 16. In the region of the cylinder33, the path 16 is centered on the roller axis over an arc of 90 andruns parallel to the surface envelope of the roller-shaped magneticarray whereby the time of contact between toner and Xero graphic layeris extended.

By virtue of the abovedescribed mechanism for supplying toner to thexerographic layer, a strong and intensive treatment of the latentelectrostatic image with the toner is ensured on the one hand and, onthe other hand, the Xerographic layer is in no way adversely affected byits contact with the yieldingly cohering carrier particles; since thesecarrier particles are lost in but slight amounts from the magnet roller,substantially all of the toner is transferred to the xerographic layer.

A container 22 for released carrier particles is located under the guidepath 16, the carrier particles falling into it through openings in theguide path 16. A handle 34 of the container projects laterally from thehousing 1, so that the container 22 can be removed and the collectedtoner particles can be returned to the supply container 18.

A set of magnets 23 are mounted on a partition 24 to strengthen theradially directed magnetic field of the array 20, 21 behind the sectionin which this array transmits toner to the xerographic layer. Theseadditional magnets are so oriented as to help erect the developeraccumulations on the circumference of the magnet roller 20, 21, therebycounteracting the deformation or flattening these accumulations whichoccur to a greater or less extent on contact with the xerographic layer.In the.

presence of a magnet roller which has :a unipolar field over its Wholecircumference, these additional magnets could be constructed aspermanent magnets; the magnets 23 of the present embodiment, however,are each constructed as electro-magnets with a reversible exciterwinding 123 so that their polarity can be adjusted according to theposition of the magnets 21 in the magnet drum. To this end, as shown inFIG. 2, the windings 123 are energizable over two commutator segments121', 121" on the shaft 120 of roller 33, a brush 122 contacting thesesegments while being connected to one lead of the energizing windings123 whose other lead is grounded. In FIG. l a position of the magnets 21is shown in which their north poles are facing the additional magnets23. To increase the field produced by these poles, the additional magnet23 must be so excited that the pole facing the magnets 2t), 33 is asouth pole. 'If the magnet roller is now rotated through about thepolarity of the additional magnets 23 is reversed. The brush-likecharacter of the developer accumulations on the circumference of themagnet roller is thus renewed by the additional magnets 23 on eachrevolution of the roller.

In order to obtain srnall apparatus dimensions, the invention provides agenerally V-shaped construction of the guide path 16, with the magnetroller 20, 21, 33 disposed in the lower part of the apparatus betweenthe remaining devices of the apparatus. The partition 24 carrying themagnets 23 separates the fusing device from the other parts of theapparatus.

The copy sheet is guided through the fusing device over a plate 25,which is perforated by being provided with openings 26. A partial vacuumis produced at these openings by a connection of the space 27 beneaththe guide plate 25 to the suction side 28 of a blower 29. This ensuresthat the layer support is guided on the guide plate 25 in a at conditionwithout the use of other guide means. This partial vacuum also has thepurpose of extracting the fumes given off in the fusing of the pigmentparticles, so that they cannot reach to the other parts of theapparatus.

For fusing in the pigment particles the guide plate 25 can be heated, asby being equipped with electric heating coils 25. Radiators 30 areprovided above the guide plate 25, either instead o-f or in addition tothe heating elements in the guide plate 25, whose heat is directed byreflectors 31 towards the copy sheet guided on the guide plate 25.Further guide elements 32 are provided at the ends of the guide plate 25in front of the exit slot 5, in the form of one or preferably moredriven rollers or Wheels operating only on the edges of the sheet. Theplate 25 is so arranged as to form a virtual extension of the rising legof the V-shaped guide path 16, so that the copy is guided slopinglyupwardly toward the exit slot 4.

What I claim is:

1. An apparatus for ydeveloping latent electrostatic images present on aphotoconductive layer, comprising supporting means for guiding a sheetcarrying said layer along a predetermined path, feed means for advancingsaid sheet along said path, a rotatable horizontal shaft extendingtransversely above said path, an array of permanent bar magnets -on saidshaft having their extremities located on a cylinder surface centered onsaid shaft, said supporting means including an arcuate elementsubstantially concentric with and spaced `from said cylinder surface, asource of magnetic developing particles disposed above said path,distributor means directly above Said array adapted to direct particlesom said source in a steady stream toward said shaft whereby brush-shapedaccumulations of particles are formed at the poles of said magnets asthe latter pass underneath said distributor means, said distributormeans extending over substantially the entire length of said array, anddrive means for rotating said shaft with said magnets, therebydisplacing said accumulations in a wiping motion across thephotoconductive-layer surface of the advancing sheet.

.2. An apparatus according to claim l wherein all of said bar magnetsextend radially and parallel to one another in a common axial plane ofsaid shaft.

3. An apparatus according to claim 2 wherein a plurality of adjacentones of said magnets are polarized in the same sense.

4. An apparatus according to claim 1 wherein said array furthercomprises a cylindrical non-magnet sleeve concentrically surroundingsaid shaft, said bar magnets penetrating said sleeve and terminating ushwith the outer surface thereof.

5. An apparatus according to claim 1, `further comprising a containerunderneath said arcuate element, said element being apertured at itslowest point for admitting spent particles into said container.

6. An apparatus according to claim l, further comprising stationarymagnet means positioned adjacent a surface portion of said array remotefrom said path for establishing an accumulation-erecting magnetic fieldat said surface portion.

7. An apparatus according to claimI l6 wherein said stationary magnetmeans comprises a series of electromagnets and commutator means yforperiodically reversing the polarity of said electromagnets insynchronism with the rotation of said shaft.

8. An apparatus according to claim l, further comprising a housing, apartition dividing said housing into two chambers, said array beinglocated in one of said chambers, fusion means in the other of saidchambers above the level of said array for xing the developed iniage bythermally bonding the adhering particles onto the photoconductive layer,said path sloping upwardly through said partition from said array tosaid Ifusion means, and stationary magnet means carried on saidpartition above said path in an axial plane of said cylinder surface forestablishing an accumulation-erecting magnetic field at a locationremote Ifrom said path.

9. An apparatus -for developing latent electrostatic images present on aphotoconductive layer, comprising supporting means for guiding a sheetcarrying said layer along a predetermined path, feed means for advancingsaid sheet along said path, a rotatable array of permanent bar magnetspositioned `for rotation about an axis above Said path with suicientclearance to leave an air space between it and said layer, saidsupporting means comprising an arcuate element positioned below saidarray and concentric with said axis, a source of magnetic developingparticles disposed above said path, distributor means adjacent saidarray adapted to direct particles from Said source in a steady streamtoward said array at a lo- 6 cation remote from said path wherebybrush-shaped accumulations of particles are formed at the poles of saidmagnets as the latter sweep past said distributor means, and drive meansfor rotating said array in a manner displacing said accumulations in awiping motion across the photoconductive-layer surface of the advancingsheet.

10. An apparatus for developing latent electrostatic images present on aphotoconductive layer, comprising supporting means for guiding a sheetcarrying said layer along a predetermined path, feed means -foradvancing said sheet along said path, a rotatable non-magneticcylindrical body positioned above said path for rotation about an axis,permanent-magnet means in said body having a plurality of spa-ced-apartpoles terminating ush with the surface of said cylindrical body, saidsupporting means comprising an arcuate element concentric with said axisand spaced from said surface While extending over an arc ofsubstantial-ly 90 therearound, a source of magnetic developing particlesdisposed above said path, distributor means at said source `forcascading a stream of particles from said source onto said surface at alocation thereon forwardly along said path of an axial plane of saidbody substantially bisecting said arcuate element whereby brush-shapedaccumulations of particles are formed at said poles and sweep said sheetat said arcuate element and particles falling onto non-magnetic portionsof said surface are cast onto said sheet, and drive means for rotatingsaid body.

ll. An apparatus for reproducing a master copy carried by a master sheeton a copy sheet carrying a photoconductive layer, comprising a housinghaving a bottom Wall, a top wall and side Walls bridging said bottom andtop walls, at least one of said side walls being provided with an inletfor said sheets; supporting means for guiding said sheets alongrespective predetermined paths within said housing, said paths includinga common rst portion adjacent said inlet, a second portion beyond saidfirst portion for said master sheet, and a third portion beyond saidfirst portion for said copy sheet, said top wall being provided with anoutlet for said master sheet in line with said second path portion;charging means at said inlet `for electrostatically sensitizing saidlayer; illuminating means in said housing along said 'first path portionfor exposing said photoconductive layer; feeding means for advancingsaid sheets along said paths whereby a latent electrostatic image ofsaid master copy is formed in said layer; separating means at thejunction of said second and third path portions `for directing saidmaster sheet along said second path portion and said copy sheet alongsaid third path portion; a rotatable array of permanent bar magnets insaid housing positioned for rotation about an axis above said third pathportion with suicient clearance to leave an air space between it andsaid layer, said third path portion comprising an arcuate element belowsaid array and concentric with said axis; a source of magneticdeveloping particles disposed above said third path portion; distributormeans at said source adapted to direct particles from said source towardsaid array whereby brush-shaped accumulations of particles are formed atthe poles of said magnets and sweep across the photoconductive layersurface of the advancing copy sheet; fixing means in said housingincluding a plurality of heating elements disposed above said third pathportion beyond said array for fusing adhering particles to said copysheet, said housing being provided with an opening adapted to pass saidcopy sheet, said third path portion terminating at said opening; andsheet-transport means in said housing at said opening for dischargingsaid copy sheet.

l2. An apparatus according to claim ll wherein said third path portioncomprises a rigid :guide plate in the vicinity of said heating elements,said guide plate being provided with a plurality of bores terminating ata surface thereof in contact with said copy sheet, further com- UNITEDSTATES PATENTS Re. 20,6610 Schacht Feb. 22, 1938 2,703,280 Butterfieldet a1 Mar. 1, 1955 2,763,204 Sims Sept. 18, 1956 8 Young Mar. 216, 1957Giaimo Mar. 26, 1957 Young Mar. 26, 1957 Lowrie Aug. 20, 1957 Grant Mar.11, 19518 Byrne Apr. 29, 1958 Reuter Sept. 16, 1958 Giaimo Oct. 7, 19518Kulesza Apr. 278, 1959

